The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Balance shafts are used to balance free forces of inertia or free mass moments of inertia; in in-line engines with four cylinders, the forces of inertia of the second order. For this purpose, two balance shafts are required which rotate in opposite senses at twice the speed of the crankshaft.
Balance shafts are either accommodated in a separate housing which is fastened in the base engine or to the crankshaft bearings. Or their housing is part of the crankcase or of the engine block. An integrated balance shaft unit is then spoken of. It is known to split the respective housing or the respective housing part to be able to install the balance shafts easily and precisely. This is above all unfavorable with the integrated design because it weakens the crankcase or the engine block respectively. To avoid this, it is also known to configure the balance weights as separate components and then to thread them into a non-split housing on the installation of the balance shaft.
It is known from DE 32 11 655 A1 for a shaft with an integral balance weight to configure a second flying balance weight separately. It is first assembled after the shaft has been pushed through a non-split bearing. The second bearing is in a bearing flange which has to be assembled together with the shaft. This construction is complex and difficult to assemble. However, it above all brings about construction limitations or it requires large bearing spacings. Finally, the flying arrangement of a balance weight is not always favorable.
These disadvantages are avoided in the solution known from DE 37 05 346 A1; however, at the price of large bearing diameters. The diameter of the bearing journals of the shaft is namely larger there than the diameter of the balance weights so that the balance shaft can be pushed in the direction of its axis. If one remembers that the balance shaft reaches five-digit revolution speeds in a high-revving four-cylinder engine, it can be recognized that huge speeds occur in the lubrication gap which, if they can be controlled at all, result in considerable friction losses.